1. Field of the Invention
The present invention relates to a polymeric binder that is capable of producing opaque films with excellent properties when formulated into a latex coating composition.
2. Description of the Prior Art
Latex paint compositions generally include a pigment or contain air voids to provide opacity, and also include a film forming polymeric binder to protect and coat an underlying substrate.
Various inorganic pigment particles such as titanium dioxide, barium sulfate, calcium carbonate and carbon black, have been conventionally utilized in paper making and paint compositions. The inorganic pigment particles are generally on the order of about 0.1 to 1 micron. The opacifying effect from the pigment particles is derived from a high light scattering coefficient which is a consequence of the particle size and a high index of refraction.
Opacification has also been achieved by entrapping air in the film forming polymeric binder to provide voids in the paint film. This contributes to scattering of light and assists the latex film to achieve the required opacity.
U.S. Pat. No. 4,391,928 to Herman et al, discloses capsular opacifier systems useful in latex paint compositions. These systems have a solid hard core and a solid soft shell which can replace both inorganic pigments and film-forming agents in a paint composition. The polymeric core material capable of being encapsulated should have a glass transition temperature, T.sub.g greater than about 80.degree. C., and the shell materials should have a T.sub.g less than about 45.degree. C. The capsular opaque system is physically blended with a binder and incorporated into an aqueous latex dispersion paint composition.
U.S. Pat. No. 3,839,064 to Vincent, discloses titanium dioxide loaded microcapsular opacifier pigment products having a solid polymeric core and a solid polymeric shell. The core contains an inorganic pigment, such as titanium dioxide dispersed therein. The materials used to make the encapsulating shell are ethylenically unsaturated monomers.
U.S. Pat. No. 4,069,186 to Ramig, discloses opacified latex paints having a majority of polymer particles larger than 1000 A.degree. in diameter, and solid non film-forming polymer particles with an average diameter between about 1000-10,000 A.degree..
Also of interest are U.S. Pat. Nos. 3,423,351 to Pierce et al; 3,779,800; 3,853,579 and 3,949,138; each to Heiser; 4,226,752 to Erickson et al; 4,497,917 to Upson et al; 4,385,152 to Boyack et al; 4,267,094 to Huhn et al; 3,657,172 to Gallagher et al and 4,419,465 to Backhouse et al.